This invention relates to solid state imaging devices, and more particularly to a solid state imaging device having an optical detector section of non-crystalline silicon.
A conventional solid state imaging device comprises an optical detector section having photo-diodes arranged in a matrix form, and a scanning circuit for successively selecting signals detected by the optical detector section. One example of a conventional solid state imaging device, comprising an optical detector section matrix in combination with a field-effect transistor circuit for X-Y scanning (hereinafter referred to as "an X-Y matrix type solid state imaging device", when applicable), is disclosed in the specification of Japanese Patent Publication No. 30768/1970. Other examples, comprising an optical detector section matrix in combination with a bucket brigade device (BBD), a charge coupled device (CCD) or a CPT type charge transfer section are disclosed in the specifications of Japanese Patent Application (OPI) Nos. 1221/1971 and 26091/1972 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") and in Electronic Materials (Denshizairyo), March 1980, page 6 et seq. In these conventional devices, the optical detector section and a circuit for successively selecting signals detected by the optical detector section (including the X-Y matrix circuit, the charge transfer circuit and a switching element, namely, a field-effect transistor for delivering charges to these circuits) are arranged two-dimensionally on a single surface. Consequently, a disadvantage of the conventional devices is that its light utility efficiency per unitary area is extremely low, i.e., only a relatively small part of the semiconductor surface area is used for detecting light.
Recently, a solid state imaging device for a multilayer structure has been proposed which is obtained by superimposing a photoconductive element on the scanning circuit. A solid state imaging device comprising a photoconductive element is superimposed on an X-Y matrix type scanning circuit using field-effect transistors (FET's) is disclosed in the specification of Japanese Patent Application (OPI) No. 91116/1974. A solid state imaging device comprising a vacuum-evaporated polycrystalline film using the hetero-junction of compound semiconductors in Groups II-VI formed on a BBD or CCD type scanning circuit is disclosed in the specification of Japanese Patent Application (OPI) No. 2777/1980. These devices have the advantage of enlarging the light detecting area of the imaging device.
Attempts have been made to use non-crystalline silicon for solar cells or electrophotographic sensitized materials. The term "non-crystalline silicon" as used herein is intended to refer to silicon not all of which have a periodic atomic arrangement and which is different from that which has a regular atomic arrangement. Accordingly, conventional non-crystalline silicon has poor photoelectric characteristics because of its lack of regularity in the arrangement of atoms. However, it has been found that a non-crystalline silicon containing hydrogen and/or fluorine has a large photoconductivity characteristic with a relatively high resistivity (10.sup.8 to 10.sup.9 .OMEGA.-cm). Hydrogen and fluroine decrease the gap state of electrons and holes in the energy gap of non-crystalline silicon. A more important finding is that valence electron control can be effected for non-crystalline silicon similarly as in the case for crystalline silicon (as disclosed in Solid State Communication by W. E. Spear and P. G. LeComber, Vol. 17 (1975), page 1193 et seq.). A significant amount of attention has been paid to the characteristics and applications for non-crystalline silicon particularly to its application to photovoltaic devices as described in Applied Physics Letters by D. E. Carlson and C. R. Wronski, Vol. 28 (1976), page 671 et seq.
Japanese Patent Application (OPI) No. 39404/1980 describes the use of non-crystalline silicon as a photoconductive element in the above-described multilayer structure solid state imaging device. As described there a single layer of non-crystalline silicon is electrically connected to the source or drain electrode of a field-effect transistor in an X-Y matrix type or charge transfer type scanning circuit which is combined with MOS field-effect transistors arranged in a matrix form, and a transparent electrode is formed on the single layer of non-crystalline silicon.